Currently, at least more than 30 countries worldwide involve in national nanotechnology projects. Nanotechnology integrates various technologies including mechanics, electronics, optics, material science, chemical engineering, fabrication, metrology, biomedical engineering, and microelectromechanical systems (MEMS). With the progress of nanotechnology applied to industrial technologies, the requirements of high precision and resolution in product manufacturing as well as in alignment of machine parts are continuously increasing. In particular, precise planar positioning and in-plan moving measurement technology are crucial in semiconductor, optoelectronic, mechanical processing, and biotechnological industries.
For researching the physical or chemical properties of nanometer-scale structures, a powerful tool is needed for observing the nanostructures. A commonly used tool is the scanning probe microscope. Such kind of instruments needs scanning and positioning platforms with high precision, high resolution, and long scanning range. The measurement and monitoring of displacement is widely applied to such platforms. Nanometer positioning includes driving, sensing, and feedback technologies; and precise measurement of displacement is an indispensable part in sensing technology. Thereby, the measurement technology for displacement can be regarded as the key technology for developing nanotechnologies.
FIG. 1 shows a schematic diagram of an apparatus for measuring displacement according to the prior art. As shown in the figure, the apparatus for measuring displacement is published by R. Dandliker and J.-F. Willemin in 1981. (Refer to “Measuring microvibrations by heterodyne speckle interferometry”, Optics Letters, Volume 6, Issue 4, Apr. 1, 1981, Pages 165-167) The apparatus for measuring displacement according to the prior art comprises a laser 11, a spectroscope 13, a plurality of acousto-optic modulators 14, a plurality of reflectors 15, a plurality of lenses 16, a grating under test 17, and a photodetector 18. The laser 11 emits a beam 12A, which is split into a beam 12B and a beam 12C by the spectroscope 13. The beams 12B, 12C are incident to the acousto-optic modulators 14, and then incident to the reflectors 15, which determine the path of the beams. Afterwards, the lenses 16 focus the beams onto the grating under test 17. The grating under test 17 diffracts and splits the beams 12B, 12C. Overlap and interfere the beams 12D, 12E diffracted by the beams 12B, 12C, and then propagate the beams 12C, 12D to the photodetector 18, which receives the interference signal of the two diffracted beams. Thereby, when the grating 17 shifts, the displacement thereof can be calculated. However, because the apparatus for measuring displacement according to the prior art uses the acousto-optic modulator as the generator of the heterodyne light source, the huge size of the acousto-optic modulator inhibits the system from miniaturization.
Accordingly, the present invention provides an apparatus for measuring displacement, which is small, facilitating miniaturization of the apparatus for measuring displacement. In addition, the amplitude of vibration can also be increased according to the present invention. Thereby, the problems described above can be solved.